Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Development of Molecular Spectroscopic Sensors for Measurement

of Antioxidant Capacıty in Food Extracts and Serum
Reactive oxygen species (ROS) attack various biological macromolecules (proteins, enzymes, DNA etc.) under ‘oxidative stress’ conditions to give rise to a number of diseases and cancer. The best way to combat such health risks is to balance these ROS through diet by the consumption of foods rich in antioxidants. Antioxidants are substances that delay or prevent the oxidation of cellular oxidizable substrates. Recently the importance of removing excessive active oxygen species from living organisms is becoming increasingly recognized, together with a growing interest in finding antioxidants that can scavenge reactive oxygen species. The aim of the developed molecular spectroscopic sensors are to resolve shortcomings and limitations of the available methods in literature for the determination of total antioxidant capacity (TAC) of food extracts and biological samples. The widely used CUPRAC (CUPric ion Reducing Antioxidant Capacity) method was originally developed and introduced to world literature by our research group. In this context, a CUPRAC-based molecular spectroscopic sensor was developed for the determination of TAC of food extracts and biological samples so as to extend the range of application of the CUPRAC method.
In this thesis work, low-cost and widely applicable sensor-based spectrophotometric methods (optical sensor-based CUPRAC method and fiber-optic reflectometric CUPRAC sensor) were developed for the total assay of antioxidants in food extracts and biological samples. Nafion is a perfluorosulfonate polymer in which hydrophilic perfluorinated ether side chains terminate with sulfonate groups, which are periodically attached to the hydrophobic perfluoroethylene backbone. Absorbance or reflectance values of the final products formed from the testing reactions on the derivatized Nafion chemical sensor were measured, and correlated to antioxidant capacities of the analytes.
As the basis of the developed optical sensor-based CUPRAC method, the chromogenic oxidizing reagent of CUPRAC method, copper(II)-neocuproine (Cu(II)-Nc) complex, was immobilized onto a cation-exchanger film of Nafion, and the absorbance changes associated with the formation of the highly-coloured Cu(I)–Nc chelate as a result of reaction with antioxidants were measured at 450 nm. According to another developed sensor-based antioxidant capacity method, fiber-optic reflectometric CUPRAC sensor, the reflectance changes associated with the formation of the highly-coloured Cu(I)-Nc chelate on the Nafion as a result of reaction of Cu(II)-Nc reagent with antioxidants were measured at 530 nm using miniature reflectance spectrometer. Thus, absorbance and reflectance of the sensor membranes were measured at different wavelengths. As a district difference from absorptimetric sensor, the reflectometric sensor principle can be applied to non-transparent opaque media.
The trolox equivalent antioxidant capacity (TEAC) values of various antioxidants (vitamins C and E, polyphenolics, thiol type antioxidants) using the developed optical sensor-based CUPRAC assay and fiber-optic reflectometric CUPRAC sensor were compared to those of the original CUPRAC assay. The developed methods were validated through linearity, additivity, precision and recovery, demonstrating that the assays are reliable and robust. The tests developed for single standard compounds were applied to their synthetic mixtures, and the found TAC values were compared to those theoretically expected by calculation thorough individual TEAC values of standart antioxidants. Finally, the developed methods were applied to complex matrices such as food extracts (fruit juices, fruit pomace and spices extracts) and biological samples (bovine serum, rat kidney and liver tissues) and obtained TAC values were validated against those found by original CUPRAC method.
As a result of this thesis work, the developed sensor based methods offer advantages over original CUPRAC method, including the potential of being used as a rapid, low-cost, and easily applicable screening tool for TAC of food extracts and biological samples, and prospects of future refinements of sensor-based methods to a kit format.